The vacuum tube assemblage in model form.
Vacuum tubes were used on the third version of the DeLorean time machine, after Emmett Brown and Marty McFly recovered it from the Delgado Mine in 1955.
In order to replace key parts from 1985 that would have existed in 1955, including the destroyed time circuit control microchip, Doc fashioned a boxframe that was attached with straps to the hood of the car, which included vacuum tubes that helped control the time circuits.